From 23e2916947940864f828505531aa130fba6d8743 Mon Sep 17 00:00:00 2001
From: Jerzy Chalupski <jerzy@getbase.com>
Date: Mon, 18 Jan 2016 16:41:07 +0100
Subject: [PATCH] Make TypeAdapters created by @JsonAdapter null-safe

---
 ...onAdapterAnnotationTypeAdapterFactory.java | 18 ++++++++-------
 .../JsonAdapterAnnotationOnClassesTest.java   | 23 +++++++++++++++++++
 .../JsonAdapterAnnotationOnFieldsTest.java    | 20 ++++++++++++++++
 3 files changed, 53 insertions(+), 8 deletions(-)

diff --git a/gson/src/main/java/com/google/gson/internal/bind/JsonAdapterAnnotationTypeAdapterFactory.java b/gson/src/main/java/com/google/gson/internal/bind/JsonAdapterAnnotationTypeAdapterFactory.java
index 77554e22..3801cfd4 100644
--- a/gson/src/main/java/com/google/gson/internal/bind/JsonAdapterAnnotationTypeAdapterFactory.java
+++ b/gson/src/main/java/com/google/gson/internal/bind/JsonAdapterAnnotationTypeAdapterFactory.java
@@ -51,18 +51,20 @@ public final class JsonAdapterAnnotationTypeAdapterFactory implements TypeAdapte
   static TypeAdapter<?> getTypeAdapter(ConstructorConstructor constructorConstructor, Gson gson,
       TypeToken<?> fieldType, JsonAdapter annotation) {
     Class<?> value = annotation.value();
+    final TypeAdapter<?> typeAdapter;
     if (TypeAdapter.class.isAssignableFrom(value)) {
-          Class<TypeAdapter<?>> typeAdapter = (Class<TypeAdapter<?>>) value;
-      return constructorConstructor.get(TypeToken.get(typeAdapter)).construct();
-    }
-    if (TypeAdapterFactory.class.isAssignableFrom(value)) {
-          Class<TypeAdapterFactory> typeAdapterFactory = (Class<TypeAdapterFactory>) value;
-      return constructorConstructor.get(TypeToken.get(typeAdapterFactory))
+      Class<TypeAdapter<?>> typeAdapterClass = (Class<TypeAdapter<?>>) value;
+      typeAdapter = constructorConstructor.get(TypeToken.get(typeAdapterClass)).construct();
+    } else if (TypeAdapterFactory.class.isAssignableFrom(value)) {
+      Class<TypeAdapterFactory> typeAdapterFactory = (Class<TypeAdapterFactory>) value;
+      typeAdapter = constructorConstructor.get(TypeToken.get(typeAdapterFactory))
           .construct()
           .create(gson, fieldType);
+    } else {
+      throw new IllegalArgumentException(
+          "@JsonAdapter value must be TypeAdapter or TypeAdapterFactory reference.");
     }
 
-    throw new IllegalArgumentException(
-        "@JsonAdapter value must be TypeAdapter or TypeAdapterFactory reference.");
+    return typeAdapter.nullSafe();
   }
 }
diff --git a/gson/src/test/java/com/google/gson/functional/JsonAdapterAnnotationOnClassesTest.java b/gson/src/test/java/com/google/gson/functional/JsonAdapterAnnotationOnClassesTest.java
index d0798412..b7b29a65 100644
--- a/gson/src/test/java/com/google/gson/functional/JsonAdapterAnnotationOnClassesTest.java
+++ b/gson/src/test/java/com/google/gson/functional/JsonAdapterAnnotationOnClassesTest.java
@@ -133,6 +133,12 @@ public final class JsonAdapterAnnotationOnClassesTest extends TestCase {
     assertFalse(json.contains("jsonAdapter"));
   }
 
+  public void testNullSafeObjectFromJson() {
+    Gson gson = new Gson();
+    NullableClass fromJson = gson.fromJson("null", NullableClass.class);
+    assertNull(fromJson);
+  }
+
   @JsonAdapter(A.JsonAdapter.class)
   private static class A {
     final String value;
@@ -215,6 +221,23 @@ public final class JsonAdapterAnnotationOnClassesTest extends TestCase {
     }
   }
 
+  @JsonAdapter(value = NullableClassJsonAdapter.class)
+  private static class NullableClass {
+  }
+
+  private static class NullableClassJsonAdapter extends TypeAdapter<NullableClass> {
+    @Override
+    public void write(JsonWriter out, NullableClass value) throws IOException {
+      out.value("nullable");
+    }
+
+    @Override
+    public NullableClass read(JsonReader in) throws IOException {
+      in.nextString();
+      return new NullableClass();
+    }
+  }
+
   @JsonAdapter(FooJsonAdapter.class)
   private static enum Foo { BAR, BAZ }
   private static class FooJsonAdapter extends TypeAdapter<Foo> {
diff --git a/gson/src/test/java/com/google/gson/functional/JsonAdapterAnnotationOnFieldsTest.java b/gson/src/test/java/com/google/gson/functional/JsonAdapterAnnotationOnFieldsTest.java
index fb5121dc..4c745ec2 100644
--- a/gson/src/test/java/com/google/gson/functional/JsonAdapterAnnotationOnFieldsTest.java
+++ b/gson/src/test/java/com/google/gson/functional/JsonAdapterAnnotationOnFieldsTest.java
@@ -200,4 +200,24 @@ public final class JsonAdapterAnnotationOnFieldsTest extends TestCase {
       this.part2 = part2;
     }
   }
+
+  public void testJsonAdapterWrappedInNullSafeAsRequested() {
+    Gson gson = new Gson();
+    String fromJson = "{'part':null}";
+
+    GadgetWithOptionalPart gadget = gson.fromJson(fromJson, GadgetWithOptionalPart.class);
+    assertNull(gadget.part);
+
+    String toJson = gson.toJson(gadget);
+    assertFalse(toJson.contains("PartJsonFieldAnnotationAdapter"));
+  }
+
+  private static final class GadgetWithOptionalPart {
+    @JsonAdapter(value = PartJsonFieldAnnotationAdapter.class)
+    final Part part;
+
+    private GadgetWithOptionalPart(Part part) {
+      this.part = part;
+    }
+  }
 }